Corrosion inhibitors in refrigeration system



ii 28, 1948. N. E. WIDELL 2,457,334

CORROSION INHIBITORS IN REFRIGERATION SYSTEM Filed Sept. 29, 1944 5 INVENTOR.

A; arm/way Patented Dec. 28, 1948 TION SYSTEM I Nils Erik Widell, Stockholm, Sweden,

or to assign Aktiebolaget Elektrolux, Stockholm, Sweden, a corporation of Sweden Application September 29, 1946, Serial No. 556,813

- In Sweden November 4, INS

8 Claims.

My invention relates to refrigeration and more particularly to absorption refrigerators of the pressure equalized type, and it is an object of my invention to provide corrosion protective means in such refrigerators.

In the drawing a hermetically closed absorption refrigeration system of the pressure equalized type is shown diagrammatically.

Referring to the figure the refrigeration system includes a generator H, a rectifier i3 and an air cooled condenser it. The generator is provided with a flue i and is arranged to be heated by a liquid fuel burner, a gas flame or an electric heater not shown in the drawing. The generator II and an absorber it are interconnected by members including an absorber vessel 26 and a liquid heat exchanger 22 for circulation of absorption liquid therethrough and therebetween. The circulation of the absorbent is affected by a' vapour lift conduit 30 which is connected in a zone 3i in heat exchange relation to the flue id. The generator II is connected by a conduit it to the rectifier It. The condenser it is connected by conduits it and It to the upper part of the evaporator H for flow of liquid from the condenser to the evaporator. The evaporator is located in the upper part of a refrigerator storage compartment not shown in the drawing. The evaporator i1 andthe absorber 59 are interconnected by members including a gas heat 'exchanger i8 and a conduit 28 for circulation of gas therethrough and therebetween. The absorber is air cooled. A pressure vessel 2! is connected to the gas heat exchanger it by a conduit 25 and further to the upper part of the evaporator H by means of a drainage conduit 2t. Weak solution is supplied to the absorbenby a conduit 36.

The system is made of iron and contains refrigerant fluid, a liquid absorbent therefor and an inert gas. These fluids may be for example, ammonia, water and hydrogen, respectively. Ammonia vapour is' distilled from solution by heating the generator Ii. Ammonia vapour is condensed to liquid in the condenser it. Liquid ammonia evaporates and diffuses into hydrogen in the evaporator l'l, producing refrigerating eifect. Ammonia vapour is absorbed out of the gas into solution in the absorber W. The mannerof operation of a refrigerating apparatus of this type is well known and will not be described more fully herein. K

For the purpose of defrosting the evaporator il I further provide an auxiliary vapour lift conduit at, the lower end of which communicates with a lower part of the boiler tube ii. The pump conduit 40 terminates at its upper end in a conduit or in anotherpart of the system from which liquid lifted by. the auxiliary pump may flow into evaporator I7.

Difiering from the generator Hand the liquid pump 3!, the vapour lift pump Ill is not arranged in direct heat conductive relation to the heating tube III. The heat supply to auxiliary pump is obtained by intermedium of an hermetically closed heat transfer system. This system includes a tube, the lower part ti of which is closed at its end and arranged in heat conductive relation to the flue w, for example, along a welded zone $2. The upper part 63 of the heat transfer system is arranged in heat conductive relation to the vapour lift pump at, for example, by welding or, as shown in the drawing, by arrangme said pump pipe within the heat transfer system. The upper end 45 of the tube is inclined as shown in the drawing and by intermedium of a flexible pipe dd connected to a condenser vessel t6, so that the system is hermetically closed. Due to the flexible pipe M, the vessel as may be ,lifted into the position designated in the drawing by dotted lines.

As a heat transfer medium the system includes a specific quantity of xylol, kerosene or the like having a high boiling point. The quantity of said liquid is such that when distilled from the heat receiving part of the system to the condenser vessel #6 a transmittance of heat by vapour lift pipe id to the evaporator i1 is obtained, which is.

sumcient for removal of the frost from the evap orator. If vessel 68 is kept in the position indicated in the drawing, the condensate of the heat transfer medium is not able to flow back into the boiler of the system but is accumulated in the vessel dd. Accordingly, aft'era certain interval of time all heat transfer medium is accumulated, the heated part of the system thus containing superheated vapour only. Due to this fact the transfer of heat to the auxiliary pump 40 is interrupted, and as a result the defrosting period of the refrigerator is automatically terminated. When a new period of defrosting is to be initiated, the vessel 86 is emptied into the boiler. In order to prevent an uncontrollable overboiling of liquid into the vessel 66, an auxiliary medium may be introduced into the system, for example, a second liquid having a lower boiling point than that of the heat transfer medium. As an auxiliary medium there may be used an ethyl alcohol.

- Though all oxygen is evacuated before the refrigerating system is filled, there appear certain 3 chemical processes in the system which may cause disturbances in the operation of the apparatus. In order to prevent such chemical processes, I include in the system according to my intrite, when a solution of, for example, sodium nitrite and a water solution of ammonia are mixed. Further the ammonium nitrite, however,

will slowly be disintegrated, said process proceeding very rapidly at high temperatures. As a result of this process there will be formed nitrogen and water. Due to the high pressure of ammonia in the refrigerating system the process is delayed and accordingly most of the nitrite enclosed in the apparatus is active as corrosion protective substance. In order to delaythe disintegration of the nitrite furthermore, I prefer to add small quantities of'alkali such as sodium hydroxide (NaOH) In certain cases it may be preferable to add small quantities of other corrosion protective means. such as chromate of sodium (micron. In order to prevent a precipitation of this substance by ammonia I prefer a concentration of chromate less than 0.05%. It may in many cases be suiflclent to have the system washed by a weak solution of chromate before filling the absorbent into the apparatus, the iron walls thus havin been passivated to a suitable extent before the filling operation.

As to the quantities of the corrosion protective means and auxiliary means I wish to mention that the absorbent may have a concentration of sodium nitrite of about 1 to 5%, and when used a concentration of hydroxide of about 0.1 to 1%, and if used a concentration of sodium chromate of less than 0.05%.

My invention may be changed and modified in many respects within the scope of the invention which is set forth in the following claims.

What I claim is:

1. In the art of refrigeration employing an ab- 4 sorption refrigerating system utilizing .ammoni as a refrigerant and water as an absorbent, that improvement in inhibiting corrosion in the system which consists in periodically lifting absorpvention corro i n Protective meal of the W9 tion solution containing an alkali nitrite as a which are soluble not only in the absorbent but corrosion inhibiting substance into an upper part also in the refrigerant or at least in a strong of the system, which solution flows by gravity solution of refrigerantinabsorbent liquid. Furdownward through parts of the system which ther, according to my invention I prefer to inare not normally supplied with absorption soluclude in the apparatus means of the type by the iii 'tion. disintegration of which "there is only formed 2. The improvementas set forth in claim 1 in soluble or gaseous products. In a refrigeration which the alkali nitrite is sodium nitrite. system containing water, ammonia and hydrogen 3. The improvement as set forth in claim 1 in I use an alkali nitrite, such as sodium nitrite which the alkali nitrite is potassium nitrite. (NaNOz) or potassiumnitrite (KNOz). In cer- 4. The improvement as set forth in claim 1 in tain cases there may be used ammonium nitrite which lire alkali nitrit 1 ammonium it t (HiNNOr). These substances are s'olubl einam """'E In the art of refrigeration employing an monia and in water and in a water solution of hermetically sealed absorption refrigeration sysammonia with a high ammonia concentration. tem utilizing ammonia as a refrigerant and wa- As an example I wish to mention that the weak a ter as an absorbent and in which solid chemical solution flowing to the absorber may have an reaction products are apt to interfere with the ammonia concentration of about 18%. The proper operation of the system, that improvement strong solution flowing to the pump 9| may have which consists of adding from 1 to 5% of an aia concentration of about 22% ammonia. The kali nitrite to the aqueous ammonia solution in V absorbent liquid elevated by the auxiliary pump 25 the system to inhibit corrosion and produce only 40 in the evaporator will meet pure ammonia or soluble or gaseous reaction products. an ammonia solution having an ammonia con- 6. In the art of refrigeration employing an centration from 90 to 98% without the nitrite hermetically sealed absorption refrigeration sysbeing precipitated. tem utilizing ammonia as a refrigerant and wa- Generally there will be formed ammonium niter as an absorbent and in which solid chemical reaction products are apt to interfere with the proper operation of the system, that improvement which comprises adding from 1 to 5 per cent of an alkali nitrite to the aqueous ammonia solution in the system to inhibit corrosion and produce only soluble or gaseous reaction prodnets, and another 'substance to stabilize the hitrite and retard its disintegration in the system,

'such stabilizing substance being added in an 40 amount insuflicient to cause any disturbances in the system.

7. That improvement as set forth in claim 6 in which said stabilizing substance is sodium chromate.

8. That improvement as set forth in claim 6 in which said stabilizing substance is sodium hydroxide.

Romances crrsn The following references are of record in the file of this patent:

. UNITED STATES PATENTS Number 

